Classifications

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  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
  • C01B33/152—Preparation of hydrogels
  • C01B33/154—Preparation of hydrogels by acidic treatment of aqueous silicate solutions
  • C01B33/1543—Preparation of hydrogels by acidic treatment of aqueous silicate solutions using ion exchangers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
  • B01J13/0091—Preparation of aerogels, e.g. xerogels
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
  • C01B33/152—Preparation of hydrogels
  • C01B33/154—Preparation of hydrogels by acidic treatment of aqueous silicate solutions
  • C01B33/1546—Preparation of hydrogels by acidic treatment of aqueous silicate solutions the first formed hydrosol being converted to a hydrogel by introduction into an organic medium immiscible or only partly miscible with water
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
  • C01B33/157—After-treatment of gels
  • C01B33/158—Purification; Drying; Dehydrating
  • C01B33/1585—Dehydration into aerogels
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
  • C01B33/157—After-treatment of gels
  • C01B33/159—Coating or hydrophobisation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/00049—Controlling or regulating processes
  • B01J2219/00162—Controlling or regulating processes controlling the pressure
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/30—Particle morphology extending in three dimensions
  • C01P2004/32—Spheres
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/32—Thermal properties

Definitions

• the present invention relates to the technical field of the production of aerogels.
• the present invention relates to a method for the production of an airgel by means of a sol-gel method.
• the present invention relates to aerogels, which are obtainable in particular by the process according to the invention, and their use, in particular as or in insulation materials.
• the present invention relates to a device for producing aerogels. Furthermore, the present invention relates to a method for producing a lyogel using a sol-gel method.
• Aerogels are highly porous solids, the volume of which can consist of pores up to 99.98%. Aerogels usually have dendritic structures with a strong branching of the partial chains, so that a large number of spaces, in particular in the form of open pores, are formed. The chains have a large number of contact points, so that a stable, sponge-like structure is formed. The pore size is usually in the nanometer range and the inner surface can be up to 1,000 m 2 / g or more. Aerogels can consist of a variety of materials, such as silicon dioxide, plastic or carbon, as well as natural organic polymers, such as alginates, or metal oxides.
• aerogels Due to their high porosity, aerogels are often used as insulating materials, for example for thermal insulation purposes, or as filter materials. At the same time, aerogels are also used as storage materials, for example for liquids or gases.
• Aerogels are nanostructured, open-pore solids, which are usually produced using a sol-gel process.
• Aerogels are usually made by drying a gel-like gel, mostly condensed silica.
• the with silicas and similar Aus Starting materials such as silica sols, silane hydrolyzates or silicates have available aerogels SiC structural units and are often referred to as silica aerogels - also called silica aerogels.
• Steven Kistler successfully synthesized silica airgel in 1931/1932. He was the first to develop a method for drying gels without shrinking them (Kistler SS, The Journal of Physical Chemistry 1932, 36 (1): Coherent expanded Aerogels, pp. 52-64).
• DE 18 11 353 A discloses a process for producing silica aerogels, wherein tetraethoxysilane (TEOS) is hydrolyzed in methanol or ethanol with a precisely metered amount of water and a catalyst.
• TEOS tetraethoxysilane
• an SiO 2 gel in the form of an alkogel is formed with the elimination of alcohol and water.
• the Alkogel is then supercritically dried in an autoclave. This process can also be used to produce organic aerogels from melamine formaldehyde resins and resorzinol formaldehyde resins.
• supercritical drying techniques the gel to be dried is exposed to temperature and pressure conditions at which the critical point of the solvent used is reached.
• the disadvantages of such supercritical drying processes are the temperature and pressure conditions and a discontinuous mode of operation.
• temperatures of at least 370 ° C and pressures of at least 220 bar are required.
• temperatures of at least 240 ° C and pressures of at least 81 bar are required.
• An alternative to this supercritical drying process is the use of compressed carbon dioxide.
• a process for drying with supercritical carbon dioxide is disclosed in EP 171 722 A, for example. Before the supercritical drying, the organic solvent becomes liquid Carbon dioxide exchanged. The supercritical drying with CO2 then takes place at much lower temperatures, for example at the critical temperature of 31.1 ° C.
• Silanes used for this include chlorotrimethylsilane and hexamethyldisilazane. This prevents Si-O-Si bridges from forming between the approaching pore walls during drying. Thus, the shrinkage that occurs is to a certain extent reversible.
• solvent with low surface tension, such as. B. pentane, the forces on the gel network are minimized. This drying process was described in 1992 by Desphande et al. developed (cf. DM Smith, R.
• the wet gel or lyogel is aged in a tetraalkoxysilane solution, such as TEOS.
• a tetraalkoxysilane solution such as TEOS.
• the tetraalkoxysilane condenses in the pores of the gel and fills it up with silicon dioxide. This makes the network more resilient, but part of the porosity is also lost (see T. Kornprobst, aerogels and photocatalysts as an example for innovative building materials, dissertation TU Kunststoff, 2013).
• the electric drying process is understood to mean processes in which the energy supply by electromagnetic waves, e.g. B. microwave drying, high frequency drying or radiation.
• electromagnetic waves e.g. B. microwave drying, high frequency drying or radiation.
• frequencies between 1 MHz and 1000 MHz are used
• microwave drying frequencies between 10 3 MHz and 10 6 MHz are used.
• the selection of the gel used, the solvent and the sample geometry must be precisely matched to the energy input so that a balance can be established between the capillary forces and the solvent evaporating inside the gel.
• DE 43 16 540 A from 1993 has so far not led to an industrial implementation of dielectric drying.
• aerogels made from subcritical drying butts are inferior to those from supercritical drying.
• Aerogels are often manufactured industrially based on the Cabot process. This is for example in DE 19 648 798 A and DE 69 903 913 T2 reproduced.
• dilute soda water glass is reacted with hydrochloric acid at 60 to 80 ° C, the gelling time, ie the time until gel formation, can be set to a few minutes.
• the gel is then tempered at 80 to 100 ° C. to solidify and mature the gel.
• the ripening time is given as 30 minutes. The gel is washed during the ripening process or afterwards until the wash water is free of electrolytes.
• Trimethylchlorosilane is used as the silanizing agent. Trimethylchlorosilane largely reacts with the water present in the hydrogel to trimethylsilanol and condenses further to form hexamethyldisiloxane, which is embedded in the pores and partially displaces the water.
• silanizing agent used is added in very large quantities. For example, 100 g of hydrogel are reacted with 140 ml of trimethylchlorosilane. Only with this ratio of hydrogel with trimethylchlorosilane is a partial conversion of the hydroxide groups on the silicon sufficient.
• silanizing agents hexamethyldisiloxane and hydrochloric acid are used in the gas stream. This leads to a partial back reaction of the hexamethyldisiloxane to trimethylchlorosilane, which can then react with the hydroxy groups of the silicon.
• Subrahmanyam et al. investigate the influence of different solvents on the structural changes during the solvent exchange and the supercritical drying of hydrogels based on a biopolymer (see Subrahman yam, R., Gurikov, P., Dieringer, P., Sun, M., Smirnova, I ., Gels, 2015, 1 (2): On the Road to Biopolymer Aerogels - Dealing wiht the Solvent, pp. 291 to 313).
• the study found significant differences between different solvents with regard to the change in pore geometry.
• the pore geometry is reduced if the solvent exchange is not carried out in one step, but in several sub-steps.
• the influence of the solvent exchange on the pore geometry can be estimated on the basis of the solubility parameters according to Hansen and thus contribute to the selection of a suitable solvent.
• the solvent exchange from water to ethanol is described by Gurikov et al. examined under the influence of compressed CO2.
• the gels used consist of Algi nat and are produced using a C0 2 -induced gelation.
• the samples have a diameter of 10 to 12 mm and are positioned in a preheated autoclave and surrounded with supercritical CO2 (120 bar, 313 K).
• Mixtures of water and ethanol are then pumped into the autoclave in several stages and the solvent exchange for 2.5 hours per stage carried out, wherein a proportion of ethanol of 30 wt .-% in the first stage, 60 wt .-% in the second stage and 90 wt .-% in the third stage is reached.
• the gels are then rinsed with 25% by weight of ethanol in CO2 in order to completely extract the water from the pores before the gels are dried over 3 hours in a supercritical manner.
• the progress of the solvent exchange is analyzed using the composition calculated from the density of the solvent. For this purpose, 5 ml samples are taken from the autoclave. Under the given conditions, the time required for the respective stages of solvent exchange was reduced from 12 hours to 2.5 hours.
• the drying time required is additionally reduced from 6 hours to 3 hours.
• the density of the gels is 0.021 g / cm 3
• the specific surface area according to BET is 538 m 2 / g
• the pore volume according to BJG is 5.96 cm 3 / g.
• the aerogels obtained have properties similar to those of the comparative samples produced by solvent exchange under ambient conditions. A direct influence of the solvent exchange under pressure on the properties of the manufactured air organs cannot be derived from the available data since different synthesis conditions are used for the different processes.
• the duration of the procedure is therefore at least 8 hours even in the best case, and this without taking washing times into account in order to keep the gel sodium-free.
• the time for gel formation and aging is approximately 2 hours using hexamethyldisilazane (HDMSO), ammonia, water, ethanol and TEOS.
• the moist gel is made hydrophobic using a mixture of HCl and HDMSO over a period of 1 hour.
• the supercritical drying time is approx. 1 hour.
• the total process times are between 4 and 6 hours.
• an object of the present invention is to be seen in providing a method for producing airgel particles which can be carried out with significantly shorter process times and preferably continuously or quasi-continuously.
• Another object of the present invention is to be able to specifically produce aerogels with defined properties, in particular also defined external shape and defined particle size.
• Another object of the present invention according to a second aspect of the present invention is an airgel according to claim 55. Further advantageous embodiments of this aspect of the invention are the subject of the related
• Yet another object of the present invention according to a third aspect of the present invention is the use of an airgel according to claim 68.
• Another object of the present invention according to a fourth aspect of the present invention is the use of an airgel according to claim 69. Further advantageous embodiments of this aspect of the invention are the subject of the related subclaim.
• Yet another object of the present invention - according to a fifth
• the subject of the present invention - according to a sixth aspect of the present invention - is a method for producing a lyogel according to claim 74.
• the present invention - according to a first aspect of the present invention - is thus a method for producing a silica airgel by means of a sol-gel method, wherein initially a lyogel is produced from a sol and the lyogel is subsequently converted into an airgel , wherein the formation of the lyogel is at least partially carried out under a pressure of more than 30 bar.
• a dimensionally stable gel can be obtained almost instantaneously manufacture.
• a sol in particular a precursor sol, ie a solution or dispersion of a precursor
• a dimensionally stable gel can be obtained almost instantaneously manufacture.
• lyogel particles and ultimately also airgel particles can be obtained. which correspond in their external shape to the drops introduced into the autoclave.
• almost spherical or cylindrical aerogels, in particular silica aerogels are accessible in the process according to the invention, which have not been known to date in the prior art.
• the duration of the process for the production of silica aerogels from gel formation to the completion of drying - if all the process steps are carried out under increased pressure - can take from 1 to 2 hours, in particular less than 1.5 hours be reduced. This is a considerable time saving compared to the prior art and thus enables a continuous or quasi-continuous manufacture of aerogels.
• the method according to the invention can also significantly reduce costs, thereby opening up further areas of application for aerogels in an industrial environment
• the spherical or cylindrical airgel particles are accessible with the process according to the invention, these are particularly suitable as thermal insulation materials, in particular in bulk, but also for incorporation into insulating plaster systems, owing to their outstanding mechanical properties or resistances and the possibility of forming dense ball packings .
• a sol-gel process is to be understood as a process in which non-metallic inorganic or organic materials or inorganic-organic hybrid materials are obtained from colloidal dispersions, the so-called sols.
• particles in the nanometer range are usually obtained from a colloidal dispersion, the sol, which subsequently form a gel by further condensation and aggregation, ie. H. a three-dimensional network, the pores of which are filled with a fluid, the fluid being either a liquid or a gas.
• a gel is a dimensionally stable, liquid and / or gas-disperse system composed of at least two components which consist at least of a solid, colloidally divided substance with long or widely branched particles, such as gelatin, silica, montmorillonite, bentonite, polysaccharides, pectins and others, and a fluid, in particular a gas or a liquid, as a dispersant.
• the solid substance is coherent, ie it forms a spatial network in the dispersion medium, whereby the particles adhere to one another through secondary or flake valences at different points, the so-called rafting points. If the spaces between the particles are filled with a liquid, a lyogel is present.
• the gel is called airgel.
• the term gel reference is made to the entry for the keyword "gels" in ROEMPP Chemie Lexikon, 9th extended and newly edited edition, Volume 2, 1999, p. 151 1.
• a lyogel is a gel, i.e. H. a three-dimensional network whose pores are filled with a liquid.
• Special cases of the Lyogel are the Flydrogel, in which the liquid is water, or the Alkogel, in which the liquid is an alcohol, usually ethanol.
• Lyogels that contain organic solvents are also known as organogels.
• a sol is a solution or a finely divided dispersion, i. H. a colloidal dispersion.
• a solution is to be understood as a single-phase mixture in which one substance - the dissolved substance - is homogeneously distributed in a second substance - the solvent.
• a dispersion is to be understood as a two-phase mixture in which a first phase with the dispersed substance, the so-called discontinuous phase, is finely distributed, in particular homogeneously distributed, in a second phase, the dispersant or the continuous phase , is present.
• the transition from solutions to dispersion is fluid and not strictly differentiated, for example colloidal solutions can neither be clearly assigned to the solutions nor to the dispersions.
• a sol is therefore preferably a solution or a finely divided, ie colloidal dispersion.
• the formation of the lyogel is carried out completely under increased pressure. In this context, it has proven particularly useful if the formation of the lyogel takes place in an autoclave, for example by introducing the sol into an autoclave.
• the method according to the invention in particular the formation of lyogels, is preferably carried out in a pressurized process medium, in particular a compressed gas or a supercritical substance or mixture of substances.
• a pressurized process medium in particular a compressed gas or a supercritical substance or mixture of substances.
• carbon dioxide and / or inert gases in particular nitrogen and / or argon, optionally in combination with other gases or substances, are used as the process medium. It has proven particularly useful if carbon dioxide and / or nitrogen, if appropriate in combination with other gases or substances, are used.
• carbon dioxide, mixtures of carbon dioxide and nitrogen or mixtures of nitrogen and ammonia are used as the process medium.
• a substance is in particular a chemical substance, i.e. to understand a chemical compound or an element with specific physical or chemical properties.
• the formation of the lyogel is carried out in compressed carbon dioxide, in particular supercritical carbon dioxide.
• the use of supercritical carbon dioxide has the particular advantage that acidification of the sol to initiate gel formation in the manufacture of silica aerogels can be dispensed with and no other electrolytes have to be added to the sol, which would then have to be removed again.
• An initiation of gel formation by shifting the pH can also be achieved by using mixtures of nitrogen or argon with ammonia, in which case the sol preferably has a pH in the acidic range.
• the pressure at which the method according to the invention is carried out can naturally vary within wide ranges. However, it has proven useful if the pressure is more than 40 bar, in particular more than 50 bar, preferably more than 60 bar, preferably more than 70 bar, particularly preferably more than 74 bar. Likewise, it can be provided in the context of the present invention that the pressure is between 30 and 300 bar, in particular in the range from 40 to 250 bar, preferably in the range from 50 to 200 bar, preferably in the range from 60 to 180 bar, particularly preferably in Range from 70 to 160 bar, particularly preferably in the range from 74 to 150 bar.
• the lyogel is produced at an elevated temperature.
• the production of the lyogel is carried out at temperatures in the range from 50 to 200 ° C., in particular 60 to 180 ° C., preferably 70 to 160 ° C., preferably 80 to 140 ° C.
• the formation of the lyogel and the transfer of the lyogel into an airgel is carried out continuously or quasi-continuously.
• the process times in particular the times of the individual process steps, can be shortened such that a continuous or at least quasi-continuous production of aerogels, in particular silica aerogels, is possible.
• the production can take place either as a one-pot process, ie in a reaction vessel, in particular an autoclave, or in successive apparatuses, in particular several autoclaves.
• the sol is a solution or dispersion of a precursor.
• a precursor is to be understood as a precursor substance from which the desired target compound, in particular an S1O 2 network, is formed by chemical reaction, in particular, for example, by hydrolysis or solvolysis and subsequent condensation.
• all compounds which are able to form a gel from precursors can be used as precursors.
• the gel formation can take place in particular at acidic pH values, a neutral pH value or a basic pH value.
• acidic pH values a neutral pH value or a basic pH value.
• the formation of money can also take place at basic pH values, for example by using mixtures of nitrogen and ammonia as the process medium.
• the precursor is selected from silica, in particular colloidal silica, silica sols, silanes, preferably tetraalkoxysilanes, siloxanes and mixtures thereof.
• silica in particular colloidal silica, silica sols, silanes, preferably tetraalkoxysilanes, siloxanes and mixtures thereof.
• the above-mentioned compounds form an optionally organically modified silicon dioxide network during hydrolysis, which is outstandingly suitable for the production of silica aerogels.
• the precursor is selected from silicas, in particular colloidal silica, silica sols, and tetraalkoxysilanes, preferably tetraethoxysilanes and / or tetramethoxysilanes. It is particularly preferred if the precursor is a silica.
• the sol has at least one solvent or dispersion medium.
• the solvent or dispersion medium is selected from alcohols, in particular methanol, ethanol, isopropanol, Ethers, dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), acetone, propylene carbonate, ethyl acetate, water and mixtures thereof.
• alcohols in particular methanol, ethanol, isopropanol, Ethers, dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), acetone, propylene carbonate, ethyl acetate, water and mixtures thereof.
• the solvent or dispersion medium consists of alcohols, in particular methanol, ethanol. Isop ropanol, water and mixtures thereof.
• mixtures of organic solvents and water, in particular ethanol and water are particularly preferred in the context of the present invention, since on the one hand the hydrolysis and condensation of the precursor compound takes place rapidly and on the other hand a proportion of organic solvents removes the solvent or dispersant from the Pores of the lyogel are promoted.
• organic solvents such as ethanol, acetone, dimethyl sulfoxide for gel synthesis offers the possibility of hydrophobicizing agents such as.
• hydrophobicizing agents such as.
• precursor solutions are preferably prepared and prepared based on silica sols, colloidal silicic acids and silica tetraethyl esters.
• silica sols and silica it is pre-silicified water glass (poly silicas) with different degrees of silicification and reduced alkali.
• the mono-silicas generally produced by means of ion exchangers are predominantly in the form of di- and tri-silicas due to condensation processes.
• the silica sols have a significantly higher degree of silicification and usually have a primary particle size between 5 and 40 mm.
• the silica tetraethyl esters (TMOS, TEOS) and potash water glasses that are often used in the manufacture of airgel the use of silica oils and silicas offers the possibility of specifically controlling the gelling and subsequent ripening process of the hydrogels.
• the silica anoparticles are generally stabilized in solutions via ionic charges.
• polysilicic acids with a low water content and a higher proportion of organic solvents is the use of alcoholic tetraethyl silicates, which, however, first have to be prehydrolyzed in order to to ensure sufficiently rapid polycondensation of the monosilicic acid formed.
• aqueous silicic acid solutions can be added after hydrolysis of the silicic acid tetraethyl ester and then gel formation can be initiated in order to produce an organogel with a low water content.
• the solvent or dispersant is water.
• the times when the lyogel is formed are extremely short.
• the formation of the lyogel under pressure within 0.1 to 60 seconds, in particular 0.2 to 30 seconds, preferably 0.2 to 10 seconds, preferably 0.3 to 5 seconds, particularly preferably 0.3 to 3 seconds.
• the sol has a pH greater than or equal to 7, in particular greater than 7, preferably greater than 8, preferably greater than 8.5.
• the sol has a pH in the range from 7 to 14, in particular 8 to 11, preferably 8.5 to 11.
• the easiest way to initiate gel formation is to shift the pH value to the neutral pH range.
• the gel formation times can be set in the range of seconds.
• At least partially aqueous dilute solutions or dispersions based on silica sols, silicas or tetraalkoxysilane are preferably added dropwise to an autoclave with compressed carbon dioxide for the production of silica aerogels or lyogels.
• the compressed carbon dioxide can be used for targeted gelation and continuous gel production of the precursor solution by shifting the pH value.
• the gelation takes place surprisingly immediately when the sol enters the autoclave if the pH is greater than 7, preferably between 8.5 and 11, is set.
• the gel formation proceeds so quickly that dimensionally stable spherical or cylindrical particles are obtained.
• the aging times of the hydrogels or organogels produced in this way are, in particular, in the range of about 30 minutes at room temperature. By increasing the temperature to 100 ° C during the dropletization phase, the aging time can be reduced to a few minutes.
• precursor solutions or brine, in particular silica solutions, with a pH value in the acidic range are used and brought into contact with a basic process medium, for example a mixture of nitrogen and ammonia. This also induces gel formation by shifting the pH.
• a basic process medium for example a mixture of nitrogen and ammonia.
• the sol usually requires a certain solids content so that a dimensionally stable gel is formed.
• the solids content of the sol is to be understood as the proportion of the sol which remains after all liquid constituents have been removed. It has proven itself within the scope of the present invention if the sol has a solids content of at least 2% by weight, in particular 2.5% by weight, preferably 3% by weight, preferably 4% by weight, particularly 5% by weight .-%, based on the sol.
• the sol preferably has a solids content in the range from 2 to 30% by weight, in particular 2.5 to 20% by weight, preferably 3 to 15% by weight 4 to 10 wt .-%, particularly preferably 5 to 9 wt .-%, based on the sol.
• a solids content in the range from 2 to 30% by weight, in particular 2.5 to 20% by weight, preferably 3 to 15% by weight 4 to 10 wt .-%, particularly preferably 5 to 9 wt .-%, based on the sol.
• the sol contains a hydrophobizing agent, in particular a silanizing agent.
• a hydrophobizing agent in particular a silanizing agent
• the sol leads in particular to the incorporation of hydrophobic groups into the structure of the lyogel. This in turn requires a more elastic gel structure, which is significantly more resilient when a solvent exchange is carried out or during drying than, for example, a pure Si0 2 structure.
• the hydrophobizing agent is selected from organosilanes, in particular monoorganosilanes, diorganosilanes, triorganosilanes, silazanes, silanoias, in particular monoorganosilanols, diorganosilanols, and mixtures thereof.
• organosilanes or organosilanols are understood to mean silanes or silanoie with organic groups, in particular hydrophobic organic groups, such as, for example, alkyl, alkenyl or aryl.
• silane is used as a hydrophobizing agent in the context of the present invention, its chemical nature can likewise vary within wide ranges. Particularly good results are obtained, however, if a silane of the general formula I
• n 1 to 3, in particular 1 or 2, preferably 1;
• R 1 Cr to C 3 o-alkyl and / or Ce to C 3 o-aryl
• R 2 halide, in particular chloride, bromide and / or iodide,
• OX with X hydrogen, alkyl, aryl, polyether and / or carboxylic acid derivative
• alkyl preferably Cr to Cs-alkyl
• the hydrophobizing agent is selected from organochlorosilanes, in particular monoorganochlorosilanes, diorganochlorosilanes, triorganochlorosilanes, methoxyorganosilanes, in particular trimethoxyorganosilanes, dimethoxydiorganosilanes, methoxytriorganosilanes, ethosilaneorganosilanes, ethilosilane ethanesilanes, ethoxiloxane organosilanes, ethosilane silanes, methylenedisilazane, trimethylsilanol, diphenylsilanediol, phenyltriethoxysilane, trimethylisopropenoxysilane and mixtures thereof.
• organochlorosilanes in particular monoorganochlorosilanes, diorganochlorosilanes, triorganochlorosilanes, methoxyorganosilanes, in
• hydrophobizing agents in particular silanizing agents
• the early use of hydrophobizing agents, in particular silanizing agents, before gel formation can influence the network structure which forms and the pore sizes which are formed can be controlled.
• the gel network can be elasticized by incorporating mono- and difunctional silanizing agents. Both can be used to accelerate a subsequent solvent exchange of the hydrogel produced.
• the sol is introduced in the form of drops in a pressurized device, in particular is dripped in and / or injected.
• nozzle can be designed, for example, in the form of a slot nozzle or a capillary and the sol can be introduced into the device by a pump, in particular a high-pressure pump.
• the introduction of the sol in the form of drops into a pressurized device thus makes it possible to obtain almost spherical lyogel particles, which remain dimensionally stable in the further process.
• the sol is pre-gelled before applying a pressure of more than 30 bar, in particular before being introduced into the pressurized device.
• a pre-gelation is to be understood as the formation of larger network structures and aggregates, although no continuous spatial network is yet to be obtained.
• the pre-gelled sol is still fluid and can be dripped or injected into a device, for example.
• the lyogel is preferably in the form of particles with a circular cross section, in particular in the form of spherical or cylindrical particles.
• a method for the production of lyogel and subsequently also airgel particles with a circular cross-section is not yet known, especially for silica aerogels.
• several reactor guides are possible in order to achieve gelation of the precursor sols.
• the precursor solution is preferably metered into a flock pressure container filled with carbon dioxide when it is prepared. Ideally, the metering is carried out in such a way that a drop chain or a gel strand is formed.
• the precursor solution is liquid or partially gelled when it enters the flap pressure container and gels completely, preferably immediately after connection, by contact with the carbon dioxide with formation of carbonic acid and a corresponding change in the pFI value.
• the solvent contained in the resulting gel such as. B. water or ethanol, is then dissolved in particular during storage of the gel in the compressed carbon dioxide, so that a dry particle, the airgel, can be obtained.
• Electrolyte additives by pH shift or addition of electrolyte to bring the precursor solutions specifically to gel formation.
• the polycondensation ability of the silicas represents the rate-determining step in the formation of a dimensionally stable, three-dimensional network. It has been shown that the use of ethanol and electrolytes enables the gels or silicas to be gelled in a targeted manner.
• Organogels with 66 vol .-% ethanol can be synthesized. These are characterized by a high rate of hydrolysis and condensation as well as the formation of a dimensionally stable organogel network.
• the precursor sol consisting of a silica sol, silica solution and / or silica tetraethyl ester, is liquid or partially gelled at the entry into the high-pressure container and completely gels immediately afterwards.
• the droplet size can in particular be controlled by the selected nozzle opening and the gelling speed and is typically in the range between 0.5 to 5 mm when using a 2 mm nozzle.
• the gel particle size can be further reduced by selecting a smaller nozzle.
• the particles which form preferably have a spherical shape and also retain the shape in the subsequent process steps.
• acids or bases can be added to the basic or acid-stabilized silica, in particular in the two-substance feed, the gelling times being able to be adjusted via the resulting pH.
• the preferred possibility is a pH shift due to the drying gas or process medium used.
• the pH can be lowered by the formation of carbonic acids, as explained above, while an increase in pH example, by using inert gases, especially nitrogen and / or Ar gon, in combination with ammonia.
• the silica can be gelled in an analogous manner to that described for the silica.
• the silica sols can be caused to gel by the use of electrolyte additives, for example polyvalent metal salts and denaturing solvents such as ethanol or acetone.
• Silicate tetraethyl esters such as tetraethyl orthosilicate (TEOS) and tetramethyl orthosilicate (TMOS) - as stated above - offer the possibility of producing organol gels with a low water content, which significantly speeds up the subsequent solvent exchange.
• TEOS tetraethyl orthosilicate
• TMOS tetramethyl orthosilicate
• he can follow a pre-hydrolysis of the metal alcoholates, which can be carried out in both the acidic and basic pH range, the formation of three-dimensional networks in acid being favored.
• Mineral acids such as hydrochloric acid can be used as catalysts for the precondensation.
• the precondensation can be accelerated by using catalysts, such as, for example, organic acids, in particular acetic acid, inorganic acids, such as hydrochloric acid, or on Lewis acids, such as, for example, titanium tetrabutanolate.
• catalysts such as, for example, organic acids, in particular acetic acid, inorganic acids, such as hydrochloric acid, or on Lewis acids, such as, for example, titanium tetrabutanolate.
• a precondensation with acetic acid at pH values from 3.5 to 4.5 and the stoichiometric content of water to tetraethyl orthosilicate from 2.5 to 3.5 produces precursor sols within a few hours, which can be gelled by pH shifts and water addition .
• the present invention relates to a previously described method, wherein
• a sol in particular a solution or dispersion of a precursor, is provided in a first method step, and
• the sol in a second process step following the first process step (a), the sol is introduced into a device pressurized with more than 30 bar, in particular is dropped or injected, whereby a particulate lyogel is obtained.
• the lyogel is aged after the formation of the lyogel. If the lyogel is allowed to age, it is preferred if the lyogel is left for a period of 1 minute to 1 hour, in particular 2 to 50 minutes, preferably 3 to 40 minutes, preferably 5 to 35 minutes, particularly preferably 10 to 20 Minutes, is allowed to age. Aging of the lyogel in particular solidifies the gel structures, so that they are significantly more stable and resistant in the subsequent drying process. The aging of the lyogel is preferably carried out at the temperature at which the formation of the lyogel takes place.
• the aging of the lyogel is carried out in the temperature range from 50 to 130 ° C., in particular 60 to 120 ° C., preferably 80 to 110 ° C.
• the pressures at which the aging process is carried out can vary within a wide range. However, it is particularly preferred in the context of the present invention if the aging of the lyogel is carried out at pressures such as during the formation of the lyogel. Due to the high pressure, a much faster gel formation and aging of the lyogel is achieved, especially in a CO 2 atmosphere.
• a lyogel in particular a hydrogel, which usually lasts at least 2 hours, to less than 15 minutes.
• a solvent exchange is carried out, in particular in a third method step (c).
• Solvent exchange may be necessary in particular to facilitate subsequent drying of the lyogel to an airgel. Water is difficult to remove in the drying process by supplying thermal energy from the usually hydrophilic network, in particular the SiO 2 network of the lyogel. This also applies if the lyogel has been made hydrophobic.
• the particles produced and preferably those with a circular cross section, in particular hydrogel particles, have a water content which usually makes drying more difficult.
• the organic solvent can be introduced into the reaction space in gaseous form and then displaces water or other organic solvents stored in the pores of the lyogel.
• the lyogel can be brought into contact with the liquid solvent, in particular to be dispersed in it or to be overlaid, and thus to a large extent, for example, by covering it several times with solvents and removing the mixture of water and / or organic solvents Solvent exchange is achieved.
• the solvent with which solvent exchange is carried out is preferably soluble in a drying gas, in particular carbon dioxide. In this way it is possible to carry out supercritical drying with carbon dioxide much faster and more gently.
• the solvent exchange in particular the water content of the lyogel is preferred to a value of less than 30% by weight, in particular less than 20% by weight, preferably less than 15% by weight less than 10% by weight, based on the lyogel, is reduced.
• the solvent exchange in particular the contacting of the lyogel with the solvent, is carried out under increased pressure.
• the solvent exchange is significantly accelerated, in particular, only a small amount of in particular gaseous organic solvents can be mixed with a compressed and pressurized gas phase, which are then still sufficient to remove water or other solvents from the pores of the lyogel to displace.
• either liquid solvent or a mixture of water and organic solvent is removed from the device during the solvent exchange or the gas phase contaminated with water is at least partially removed from the reactor and new solvent in gaseous state into the reactor introduced in order to obtain the most complete solvent exchange possible.
• the solvent exchange in particular the contacting of the lyogel with the solvent, at pressures in the range from 30 to 300 bar, in particular 50 to 250 bar, preferably 70 to 200 bar, preferably 100 to 180 bar, particularly preferably 120 to 170 bar is carried out.
• the solvent exchange is carried out at an elevated temperature. Particularly good results are obtained in this connection if the solvent exchange, in particular the contacting of the lyogel with the solvent, at temperatures above 50 ° C., in particular above 70 ° C., preferably above 90 ° C., preferably above 100 ° C, particularly preferably above 110 ° C, is carried out.
• a high temperature especially in conjunction with a high pressure, ensures that the solvent exchange is as quick and complete as possible.
• the solvent exchange in particular the contacting of the lyogel with the solvent. medium, at temperatures in the range from 50 to 180 ° C., in particular 70 to 160 ° C., preferably 90 to 150 ° C., preferably 100 to 140 ° C., particularly before 10 to 130 ° C., is carried out.
• the organic solvent it has proven useful if the solvent is selected from the group of the hydrophilic organic solvents, the hydrophobic organic solvents and mixtures thereof. It is particularly preferred in the context of the present invention if the organic solvent is soluble in carbon dioxide.
• an organic solvent is understood to mean a solvent or dispersant which has an organic group.
• the organic solvent is selected from the group consisting of alcohols, ethers, dimethyl sulfoxide, N, N-dimethylformamide, Cs to Cs alkanes and mixtures thereof.
• the organic solvent is selected from methanol, ethanol, isopropanol, dimethyl sulfoxide, n-pentane, n-hexane, n-heptane, cyclo-hexane and mixtures thereof.
• the organic solvent is brought into contact with the lyogel together with a hydrophobizing agent, in particular a silanizing agent.
• a hydrophobizing agent in particular a silanizing agent.
• the water content of the lyogel is at least 50% by weight, in particular at least 60% by weight. preferably at least 70% by weight. In this way, rapid hydrolysis and reaction is the most reactive Groups of the hydrophobizing agent, in particular the silanizing agent, given.
• the hydrophobizing agent is selected from organosilanes, in particular monoorganosilanes, diorganosilanes, triorganosilanes, silazanes, silanoien, in particular, monoorganosilanols, diorganosilanols and mixtures thereof.
• organosilanes in particular monoorganosilanes, diorganosilanes, triorganosilanes, silazanes, silanoien, in particular, monoorganosilanols, diorganosilanols and mixtures thereof.
• a silane is used as a water repellent in the context of the present invention, its chemical nature can vary within wide ranges. Particularly good results are obtained, however, if a silane of the general formula I
• n 1 to 3, in particular 1 or 2, preferably 1;
• R 1 Cr to C 3 o-alkyl and / or C ⁇ - to C 3 o-aryl
• Halide especially chloride, bromide and / or iodide
• alkyl preferably C 1 to C 5 alkyl
• the hydrophobizing agent is selected from organochlorosilanes, in particular monoorganochlorosilanes, diorganochlorosilanes, triorganochlorosilanes, methoxyorganosilanes, especially trimethoxyorganosilanes, dimethoxydiorganosilanes, methoxytriorganosilanes, ethoxyiloxiloxane, ethoxyiloxiloxane, ethoxyiloxiloxane, ethoxyiloxiloxane, ethoxyiloxiloxane, ethoxyiloxiloxane Trim thylsilanol, diphenylsilanediol, phenyltriethoxysilane, trimethylisopropenoxysilane and mixtures thereof.
• hydrophobizing agents which are preferably used during the solvent exchange thus correspond to the hydrophobizing agents which are also used in the hydrophobization or silanization of the sol.
• the precursor sol is mixed with a hydrophobizing agent, in particular a silanizing agent, and if a further hydrophobization is carried out after the formation of the lyogel.
• the hydrophobization after the formation of the lyogel results in the pores of the lyogel being rendered hydrophobic.
• the pores can be rendered hydrophobic, in particular pore silanization, with the use of further hydrophobizing agents, in particular silanizing agents.
• further hydrophobizing agents such as, for example, hexamethyldisilazane, can significantly accelerate the required solvent exchange step.
• the residual water content of the lyogels should be sufficiently high, preferably above 50% by weight, based on the weight of the lyogel.
• the pH values of the solutions or dispersion of the hydrophobizing agent, in particular of the silanizing solutions can vary depending on the hydrophobing agent used, in particular the silanizing agent.
• the silanizing agent used, in particular the silanizing agent.
• pH values greater than 8 have proven to be advantageous.
• Organic solutions such as non-polar substances (hexane), aprotic solvents or alcoholic solvents, such as, for. B. methanol, ethanol, isopropanol or the like.
• hydrophobicizing agents in particular silanizing agents, are added.
• the lyogels can be bathed in the solution or dispersion containing the hydrophobicizing agent or can be surveyed therewith, the contact times being up to 30 minutes.
• the hydrophobizing agents in particular silanizing agents, can also be mixed in a saturated or partially saturated organic solvent.
• sealed phase in particular the process medium, preferably a CO2 phase, can be used, wherein the phase can be both a subcritical gas phase and a supercritical phase.
• Non-polar solvents such as hexane, aprotic solvents such as dimethyl sulfoxide or alcoholic solvents such as ethanol are suitable as organic solvents.
• the solvents used can improve the solubility of the hydrophobizing agents, in particular the silanizing agents in the compressed CC> 2 phase. If the water repellents, in particular the silanizing agents, are sufficiently soluble in the process medium, especially in compressed CO2, the use of organic solvents is not necessary.
• a C0 2 -soluble solvent is preferably introduced into the process.
• the solvent exchange then takes place, for example, under a pressure of 80 bar and 120 ° C.
• dissolving the solvent into the CC phase is sufficient to displace the water from the pores.
• the gel which is stored in particular in an autoclave, can be overlaid with liquid solvents. This is preferably done at a pressure of 160 bar and a temperature of 120 ° C.
• the solvent exchange is carried out in several process stages, in particular in 2 to 15, preferably 3 to 10, preferably 3 to 4, process stages.
• the lyogel is brought into contact with the organic solvent several times. It is preferably specified here that at least part of a mixture of solvent and water or solvent to be replaced is removed from the reactor in each process stage and new organic solvent is introduced.
• the water content of the lyogel is below 20% by volume, preferably below 15% by volume, preferably below 10% by volume, based on the total volume of solvent - or dispersants, is reduced.
• the solvent exchange can be carried out by using water-miscible solvents, such as ethanol, methanol, isopropanol and dimethyl sulfoxide.
• water-miscible solvents such as ethanol, methanol, isopropanol and dimethyl sulfoxide.
• hydrophobic organic solvents can also be used for this process step, such as. B. hexane, pentane or cyclohexane, which can replace the stored water in the Po ren with sufficient presilanization from the lyogel.
• the solvent exchange is preferably carried out in the compressed carbon dioxide.
• the solvent is metered in under pressure in a reactor, in particular in an autoclave.
• a solvent exchange can also be carried out successfully if the solvent does not come into contact with the gel particles in liquid form. Rather, it is sufficient if the solvent dissolves in the compressed CO2 and thus penetrates the gel and displaces the water from the pores.
• the present invention relates to a method for producing aero-gel as previously described, wherein
• the sol in a second process step following the first process step (a), the sol is introduced, in particular dripped or injected, into a device pressurized with more than 30 bar, where a particulate lyogel is obtained, and
• the solvent exchange in process step (c) can take place over a period of up to 50 minutes, in particular up to 40 minutes, in particular up to 30 minutes. It is particularly preferred in the context of the present invention if the solvent exchange is carried out over a period of 10 to 50 minutes, in particular 20 to 40 minutes, preferably 20 to 30 minutes.
• the lyogel is converted into an airgel by removing the solvent or dispersion medium, in particular in a subsequent process step (d).
• the lyogel is converted into an airgel following a solvent exchange and / or a hydrophobicization of the lyogel, in particular following method step (c).
• the lyogel is brought into contact with a drying medium, in particular a drying gas or a supercritical medium, for transferring the lyogel into an aero gel.
• the drying medium is preferably carbon dioxide.
• the lyogel is brought into contact continuously or discontinuously with the drying medium, in particular the drying gas or the supercritical medium.
• discontinuous contacting the lyogel is brought into contact in a device with a predetermined amount of the drying medium over a preselected period in one device. Then the drying medium contaminated with solvent is removed and, if necessary, exchanged for fresh drying medium until the desired degree of drying is achieved.
• the drying medium sweeps over or flows through the lyogel in a device until the desired degree of drying is reached.
• the removal of the solvent is carried out at pressures of more than 50 bar, in particular more than 60 bar, preferably more than 70 bar, preferably more than 74 bar.
• the removal of the solvent is carried out in the range from 50 to 180 bar, in particular 55 to 160 bar, preferably 60 to 140 bar, preferably 70 to 130 bar, particularly preferably 74 to 130 bar.
• the temperatures at which the removal of the solvent is carried out it has proven useful if this is carried out at elevated temperatures.
• the removal of the solvent is usually carried out at temperatures above 50 ° C., in particular above 55 ° C., preferably above 60 ° C.
• an air organ can be obtained particularly quickly, particularly by supercritical drying using CO2. It is usually provided in the context of the present invention that the solvent is removed from the lyogel within 10 to 50 minutes, preferably 20 to 30 minutes.
• the present invention is preferably a method for the manufacture of an airgel as described above, wherein
• the sol in a second process step following the first process step (a), the sol is introduced, in particular dripped or injected, into a device pressurized with more than 30 bar, where a particulate lyogel is obtained,
• the method according to the invention is usually carried out with a total duration over the Process steps (a) to (d) with the implementation of process step (c) in a period of 1 to 2 hours, preferably 1 to 1.5 hours.
• the process according to the invention can be carried out either as a one-pot synthesis or process, i. H. in an autoclave. Equally, however, it is also possible for the individual steps to be carried out in a plurality of devices, in particular autoclaves, which are connected in series. In the context of the present invention, however, it is particularly preferred if all process steps are carried out under increased pressure, in particular in a CO2 atmosphere.
• the particles are preferably dried in supercritical CO2.
• the drying time of the spherical gel particles obtained, with a size of 0.5 to 5 mm, can be reduced to 10 to 30 minutes using the process according to the invention with hydrophobicization of the lyogels.
• the gas stream can be used for the targeted continuous drying of the organogels, and one-stage airgel particle production, i. H. in a reactor vessel or reactor.
• the supercritical drying can be carried out in a time window of up to 30 minutes at a pressure of 120 bar and a temperature of 60 to 120 ° C.
• FIG. 1 shows a cross section of a device according to the invention for carrying out the method according to the invention
• Another object of the present invention according to a second aspect of the present invention is an airgel, in particular according to the previously described methods, wherein the airgel is in the form of particles with a particularly essentially circular cross-section.
• the aerogels according to the invention are distinguished by a particularly circular cross section, which on the one hand significantly increases the mechanical strength and on the other hand the ability to form dense ball packs.
• the airgel particles are spherical or cylindrical.
• the aerogels according to the invention offer advantages during processing. In this way, the spherical aerogels can be mixed into powder mixtures much better. Because of their improved flowability, higher strengths with uniaxial pressure loading and higher packing density compared to conventional airgel powders, which are based on shapeless or cubic particles, the preferably spherical aerogels according to the invention can preferably be used in powder fillings or powder mixtures, such as thermal insulation plasters.
• the aerosol has particle sizes in the range from 0.1 to 10 mm, in particular 0.2 to 8 mm, preferably 0.3 to 7 mm, preferably 0.5 to 5 mm.
• the airgel particles have a monodisperse particle size distribution.
• the aero gel particles may have a polydisperse particle size distribution.
• the particle size distribution can in particular be controlled in a targeted manner by varying the injection or dropping conditions into the reactor.
• the airgel particles according to the invention are highly porous solids.
• the airgel usually has a porosity of over 94%, in particular over 95%, preferably over 96%.
• the airgel has a porosity of 94 to 99.5%, in particular 95 to 99%, preferably 96 to 98%.
• the aerogels according to the invention have high internal surfaces. It can be provided that the aorule has a BET surface area of at least 500 m 2 / g, in particular 600 m 2 / g, preferably 650 m 2 / g, preferably 700 m 2 / g, particularly preferably 800 m 2 / g , having.
• the airgel has a BET surface area in the range from 500 to 1,000 m 2 / g, in particular 600 to 1,050 m 2 / g, preferably 650 to 1,000 m 2 / g, preferably 700 to 950 m 2 / g , particularly preferably 800 to 900 m 2 / g.
• the thermal conductivity of the airgel As far as the thermal conductivity of the airgel is concerned, this can vary within a wide range. Usually, however, the airgel has very low thermal conductivities in the context of the present invention. Particularly good results are obtained if the airgel has a thermal conductivity of at most 0.025 W / mK, in particular at most 0.022 W / mK, preferably 0.020 W / mK, preferably 0.019 W / mK.
• the airgel usually has a thermal conductivity in the range from 0.012 to 0.025 W / mK, in particular 0.013 to 0.022 W / mK, preferably 0.014 to 0.020 W / mK, preferably 0.015 to 0.019 W / mK.
• the airgel has a density in the range from 0.01 to 0.60 g / cm 3 , in particular 0.1 1 to 0.55 g / cm 3 , preferably 0.12 up to 0.50 g / cm 3 , preferably 0.13 to 0.50 g / cm 3 .
• Yet another object of the present invention according to a third aspect of the present invention is the use of the above-described airgel for insulation purposes, in particular for sound insulation, electrical insulation or thermal insulation, in particular for thermal insulation.
• Yet another object of the present invention according to a fourth aspect of the present invention is the use of an airgel, as described above, for insulation purposes, in particular as or in thermal insulation.
• the airgel is used in bulk, in a powder mixture or in an insulating compound, for example an insulating plaster.
• Yet another object of the present invention - in accordance with a fifth aspect of the present invention - is a device for producing airgel under pressure, the device
• (c) has at least one outlet opening arranged on the reactor, in particular a lock, for removing liquids or solids from the reactor.
• a sol for producing a lyogel is dripped or injected into the reactor via at least one inlet opening.
• the reactor each has several inlet openings for introducing fluids, in particular liquids, namely at least one nozzle for introducing the sol into the reactor and at least one nozzle for introducing further solvents.
• the outlet opening of the reactor is preferably formed in the form of a lock in order to be able to quickly remove the lyogel or airgel from the reactor or also to perform a multiple solvent exchange by overlaying and then draining the contaminated solvent from the reactor to ensure ge.
• the device has at least one inlet and / or outlet opening arranged on the reactor for introducing and / or removing gases into and / or out of the reactor.
• the pressure in the reactor is preferably regulated via the amounts of substance, in particular in the gas phase and / or a supercritical phase and / or the temperature. Pressure regulation can take place, for example, in such a way that gas is introduced into or removed from the reactor.
• the device has a device for temperature regulation.
• the processes in the reactor and thus in the device as a whole can also be specifically influenced and controlled via temperature regulation. It is particularly possible that the reactor is heated or cooled.
• the device usually also has a control device, in particular for controlling the pressure and / or the temperature in the reactor.
• the device according to the invention can either have a reactor or, however, also have several, in particular successive and / or interconnected reactors, so that the individual process steps of the process according to the invention are each carried out in separate reactors. In this way, continuous airgel production can take place.
• Another object of the present invention - according to a sixth aspect of the present invention - is a method for producing a lyogel using a sol-gel method, the formation of the lyogel being carried out at least partially under a pressure of more than 30 bar.
• all advantages, special features and embodiments apply, which were previously mentioned as part of the method for producing an airgel in relation to the lyogel.
• the object of the present invention is illustrated below in a non-restrictive manner and by way of example with reference to the figure representations and the exemplary embodiments, in an exemplary and non-restrictive manner.
• the reactor 2 has a plurality of inlet openings, in particular nozzles 3, 4, 5 for the inlet of liquids and / or gases, and has an outlet opening 6 for removing substances from the Reactor 2, such as aerogels or lyogels or liquid solvents.
• a precursor solution 7 is provided, which is placed in a container 8 and is introduced or injected into the reactor 2 by means of the inlet opening 7, in particular a nozzle.
• the precursor solution 7 is in particular an aqueous solution of a silica, a silica sol or a silane hydrolyzate, which has a pH in the basic range, preferably between 8.5 and 10.
• the reactor 2 preferably has an atmosphere 9 of supercritical CO2, in particular with a pressure of 80 to 120 bar and a temperature of 120 ° C.
• an almost spherical and dimensionally stable lyogel 10 is formed directly from the sol.
• the lyogel particles 10 collect on the bottom of the reactor 2 and can either be removed from the reactor 2 or processed further in the reactor.
• a solvent exchange is preferably carried out with simultaneous hydrophobization of the lyogel 10 by means of a suitable organic solvent and a hydrophobizing agent, in particular a silanizing agent. Solvents and hydrophobic agents are introduced into the reactor 2 via the inlet opening 5.
• the organic solvent is soluble in CO2 in order to to enable a comprehensive supercritical drying with CO2.
• Gases such as CO2 can be introduced into the reactor via the inlet opening 5 and, if appropriate, also removed again.
• the lyogel 10 is dried or in particular by first draining the solvent through the outlet opening 6 and then carrying out a supercritical drying of the lyogel by means of CO2, so that an airgel is obtained.
• Silica aerogels are made from silica and examined for their properties:
• the silica is produced from soda water glass using an ion exchanger.
• the solids content is adjusted to 5 to 10% by weight, preferably 7 to 8% by weight.
• To store the silica it can be stabilized to a pH of 1 -2 using HCl.
• the pH of the silica is then adjusted to a pH of 8.5 to 10.5 a few minutes before use by adding NH3.
• the silica produced is dropped into a container pressurized with CO2 by means of a high-pressure pump. Depending on the capillary chosen, drops with a diameter of 2 to 6 mm are formed.
• the pressure inside the container can be varied between 30 bar and 300 bar for gelation, at a minimum temperature of 60 ° C. The gelation takes place as soon as the silica enters the pressure vessel by changing the pH value due to the CO2 diffusing into the water.
• the hydrogel particles in spherical form collect on the bottom of the container.
• the water in the hydrogels disrupts the drying process and must therefore be replaced by a suitable C0 2 -soluble solvent.
• the pressure is preferably set in the supercritical range, for example to 140 bar, and ethanol with 5% hexamethyldizisilazane (HDMZ) is metered into the container.
• HDMZ ethanol with 5% hexamethyldizisilazane
• the gels contain less than 5% water and can be dried supercritically.
• the pressure in the column is preferably varied between 100 to 160 bar, preferably 120 bar and 160 bar, for 45 minutes, at a container temperature of 80 ° C. to 120 ° C.
• the supercritical drying can take place either continuously or discontinuously.
• the gel is brought into contact with a defined amount of the drying medium, in particular carbon dioxide, in the column and, after an adjustable dwell time, the drying medium enriched with solvent is partially or completely removed from the column and replaced by fresh drying medium, the process being repeated is repeated until the desired degree of dryness is reached.
• the column can be continuously flushed with the drying medium, in particular carbon dioxide, during the continuous drying.
• the pressure can either be kept constant or can be varied, in particular can be varied periodically. After completing the drying step, dry spherical aerogels can be removed. 2. Properties of aerogels
• silanizing agents prior to gel formation has positive effects on the gel matrix that forms.
• the silanizing agent is built into the Si-O network that forms. This leads to a partial elasticization of the network, which is reflected in smaller pore radii and an accelerated solvent exchange and less shrinkage.
• the airgel samples produced are stored in liquid water and 98% relative atmospheric humidity. The result shows that although pre-silanization is advantageous for the structure, it is often not sufficient for complete silanization. Resilanization during the drying process means that only a small amount of moisture is absorbed in the pores of the aerogels over a period of 4 weeks in water.
• Samples A5 to A8 are pre-silanized using hexadimethyldisilazane at pH values of 7.0; in contrast, samples H-5 to H-8 are pre- and post-silanized.
• the average pore radius can be varied between 30 and 15 nm.
• the shrinkage due to the drying was reduced in the samples with pre- and post-silanization.
• the H-8 has the lowest shrinkage and the highest porosity.
• the hot disk sensor consists of a nickel double spiral, which serves both as a heating source and for measuring the temperature rise during the measurement.
• the measured values of the sorption measurement carried out analogously are shown together with the hydrophobicized airgel H-8 in FIG. 2F. Both aerogels show a similar course of the isotherms. A constant value of the adsorbed volume is also not achieved. This behavior shows that the P300 also contains pores that are not detected by the sorption measurement and the evaluation according to BET or BJH. In addition, the P300 has an extended flysteresis, which is caused by an increased flooding of the desorption of nitrogen.

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